Lubricating grease compositions containing n-acyl-p-amino phenols



United States Patent LUBRICATING GREASE COMPOSITIONS CON- TAININGN-ACYL-p-AMINO PHENOLS David W. Young, Westfield, and Delmer L. Cottle,Highland Park, N. J., assignors to Esso Research and EngineeringCompany, a corporation of Delaware No Drawing. Original application June4, 1954, Serial No. 434,676. Divided and this application January 13,1955, Serial No. 481,696

7 Claims. (Cl. 25242.1)

The present invention relates to the stabilization of organiccompositions normally subject to oxidative changes. More particularly,the present invention relates to the stabilization of organiccompositions containing, besides carbon, at least the elements ofhydrogen and oxygen, with N-acyl para aminophenols wherein thehydrocarbon residue of the acyl group has at least two carbon atoms.Still more specifically, the present invention relates to thestabilization of organic compositions comprising in particular organicacids, such as fatty acids, and their derivatives, including the mono,diand polyesters, soaps, glycerides, and the like.

The present application is a division of Serial No. 434,676, filed June4, 1954; that application is a continuation-in-part of Serial No.186,318, filed September 22, 1950, now abandoned, and also of Serial No.334,725, filed February 2, 1953, now abandoned; the latter in turn is acontinuation-in-part of Serial No. 237,476, filed July 18, 1951, nowabandoned.

The compositions of the present invention find utility in the field oflubricants, i. e. as lubricating Oils and greases. These include simpleand complex esters of long chain fatty acids with alcohols and glycols,mineral oil and ester oil compositions thickened into solids andsemi-solids with thickening agents, such as soaps of long chain fattyacids, and the like.

The stabilized compositions of the present invention also find utilityin the field of edible foods, such as animal fats and oils, vegetablefats and oils, long chain fatty acid soaps and the like, all of whichtend normally to be subject to oxidation changes. Animal and vegetablefats and oils consist to a substantial extent of simple and mixed estersof poly alcohols, in particularly of glycerine. Thus triolein,tripalmitin, tristearin, trimyristin, and interand intramolecularmixtures of these esters, as well as other fatty acids, i. e. linoleicand linolenic, are components of such foods as lard, butter, cocoanutoil, soybean oil, hardened fats, such as bydrogenated cotton seed oil,olive oil and the like. In accordance with one; embodiment of thepresent invention, readily oxidizable oils, fats, fatty oils, fattyesters, fatty acids and salts of fatty acids are stabilized againstrancidity and deterioration with minor amounts of 'N-acyl p-aminophenolswherein the hydrocarbon residue of the acyl group has at least twocarbon atoms.

In one embodiment, the present invention relates .to lubricating greasecompositions. Particularly this embodiment relates to lubricating greasecompositions having outstanding oxidation resistant properties. Moreparticularly, this embodiment of the invention relates to a lubricatinggrease composition comprising a lubricating grease containing combinedtherein a minor proportion of an acyl p-aminophenol as an oxidationinhibitor.

It is a common practice in the art of. manufacturing lugricating greasecompositions to increase the resistance of the greases to oxidation byincorporation of substances known as oxidation inhibitors. There arevarious oxi dation inhibitors known to the art, examples being suchmaterials as phenyl alpha naphthylamine, phenyl beta naphthylamine,phenolic type compounds, complex amine intermediates and the like. Ithas now been found that grease compositions containing minor amounts ofacyl p-aminophenols have outstanding characteristics in regard tooxidation stability and also superior retention properties. a

'The acyl p-amino phenolic derivatives contemplated for use in thegrease compositions of this invention have the following generalstructure:

H O HO lake wherein R is an alkyl group containing from 2 to 24 carbonatoms, preferably non-benzenoid in nature, and R and R are hydrogenatoms or alkyl groups.

The preferred embodiment of the invention contemplates the use ofcompounds according to the formula above where R is an alkyl groupcontaining from 10-18 carbon atoms and R and R are hydrogen, i. e., theacyl p-amino phenols. However, the alkylat-ed acyl p-amino phenols,exemplified by the formula above, R and R being alkyl groups containingfrom 1 to 20, preferably 4 to 15 carbon atoms, are also verysatisfactory as oxidation inhibitors. Compounds such as N-n-valeryl-4-amino-3 pentadecyl phenol, (N-n-pentanoyl-4-amino-3 pentadecylphenol), N-n-propanoyl-4-amino-3 pentadecyl phenol,'N-n-pentanoyl-4-amino-2,6, di-tertiary butyl phenol,N-n-hexoyl-4-amino-2 hexyl phenol are examples of the alkylatedacyl-p-amino phenols operable.

The preparation of these acyl p-amino phenols may be achieved byadmixing the desired acid or acid chloride with p-amino phenolandheating the mixture under proper conditions. The reaction progressessmoothly, splitting olf water (or hydrogen chloride) and giving thedesired acylated aminophenols which may be purified by any of thevarious methods known to the art such as distillation, crystallization,extraction, etc.

As the acidic constituent of the reaction mixture, any organic acidcontaining from 3 to 24 carbon atoms may be combined with the p-aminophenol. The compounds especially preferred as oxidation inhibitors,however, are

those long chain fatty acids or fatty acid chlorides containing from 11to 19 carbon atoms per molecule.

It may be found convenient in some instances to prepare the greases ofinvention in such manner that the desired acyl p-amino phenol is formedin situ. This preparation may be accomplished in one of two manners:

(1) To a heated oil solution containing the preformed soap there may beadded the calculated amount of a p-aminophenol. The desired acid or acidchloride may then be added, the formation of the acyl p-aminophenoltaking place upon the addition of the acidic constituent. The acylatinggroup and the soap forming acid may or may not be the same; or

(2) There may be added to a heated oil solution a calculated amount of along chain saturated acid or a mixture of these acids. To this mixtureis added an amount of the desired metallic hydroxide suflicient to formthe proper percentage of soap and to leave some unreacted acid present.p-Aminophenol is then added and reacts with the free acid to give theacyl p-aminophenol, the amount of the aminophenol added being suflicientto form the desired quantity of the antioxidant. In this procedure theacylating group and the soapforming acid are necessarily the same acid.

In both instances of the preparation of the antioxidant in situ, afterthe reaction is completed the mixture is stripped with heat, and wateris removed to form the stabilized grease.

Thegrease compositions of this invention may be prepared by dispersingany of the common grease making soaps in a lubricating oil, usingsufficient quantities of the desired soaps to form grease compositionsofvarying consistencies. Any of the various alkaline earth or alkalimetals such as calcium, strontium, barium, potassium, sodium, or lithiummay be used to form the soaps of any of the Well known grease makingacidic materials, exemplified by hydrogenated fish oil acids, stearicacid, hydroxy stearicacid, oleic acid, palmitic acid, lauric acid,tallow, cocoanut oil, the saturated or unsaturated glycerides of thevarious fatty acids or mixtures-of these in any'proportion.

The oil base in which the above mentioned soaps may be dispersed may beselected from either the natural occurring mineral oil distillatestreated by any of the modern refinery technique or a syntheticlubricating oil such as the long chain esters .of aliphatic acids,esters of dibasic acids such as sebacates, adipates and the like,polymerized cracked wax, acylated aromatics, polyglycol esters,polyglycol ethers, polyglycol ether esters, and the like.

The grease composition'of this invention may be prepared by any of theprocedures with which the art of grease manufacture is well familiar.For instance, a preformed soap may be admixed with a small proportion ofthe desired lubricating oil base, heated to the melting point of thesoap with stirring and the remainder of the mineral oil then added andallowed to cool. Or, if it is desired, the soap may be prepared in situby ad- -mixing with a minor proportion of the oil the desired amount'ofthe acidic material, forming the soap by adding the calculatedequivalent of the desired metallic hydroxide, raising the temperature ofthe mixture to drive off the water formed, adding the remainder of themineral oil and allowing it to cool to handling temperature. Thesemethods are well known in the art and do not form a part of thisinvention.

The desired amount of the oxidation inhibitor maybe added to the greasecomposition at any stage of its manufacture. It is usually preferred toadd from 0.25% to 2% of the acyl p-aminophenol with 0.5 to 1% beingespecially preferred in most formulations. If the oxidation inhibitor isbeing added to a preformed grease it is advantageous to first dissolvethe acyl p-aminophenol in a naphthenic oil and then incorporate thesolution into the grease composition that is slightly warm. When itisdesired to add the acyl p-aminophenol during the preparation of thegrease composition this pre-solubilization is unnecessary and thecompound may be added preferably after the soap has been formed.

In the preferred embodiment of this invention the following procedure isused:

A portion of the lubricating oil is admixed with the fatty material in agrease kettle equipped for heating by a steam jacket or by a directflame. ,A solution of the desired metal, usually in the form of ametallic hydrox ide, is then added to the mixture with stirring. 'Thetemperature of the mixture is then raised to about 400 to 420 F. At thatpoint the balance of the lubricating oil and the additive materials areadded. Heat. is then stopped. The resulting composition is then pancooled or cooled in a continuous grease cooler according to standardprocedures.

EXAMPLE I A lubricating grease composition, according to the concept ofthis invention, was prepared by the procedure detailed above from thefollowing formulation:

29.00% rapeseed oil 5.92% sodium hydroxide 1.00% petroleum sulfonate1.00% N-lauroyl p-aminophenol 63.08% Coastal distillate having aviscosity at 210 F. of

55 S. U. S. and a V. I. of 50.

EXAMPLE II A second experimental grease was prepared by the procedureand formulation used in Example 1 except that N-myristoyl p-aminophenolwas the oxidation inhibitor added.

EXAMPLE III In the third experimental grease prepared as Examples I andII above, N-stearoyl p-aminophenol was used.

EXAMPLE IV In the fourth experiment a grease was prepared as in ExamplesI to III above, using N-n-valeryl-4-amino-3- pentadecyl phenol as theanti-oxidant.

EXAMPLE V According to the following formulation a preformed syntheticester base grease was prepared using known procedures.

76.75% di-Z-ethyl hexyl sebacate 22.75% lithium stearate .50% zincnaphthenate stant temperature, usually 100 C. under an oxygen pres sureof 110 p. s. i. The loss in oxygen pressure is a -function of the.oxidation. resistance of the. grease, that is to say, a grease. that ishighly resistant to oxidation will show a small pressure. drop after anextended period of test time. The results of the. tests on theseexperimental greases. are. shown in Table I below. Included in the dataon Table I are comparative test data obtained by subjecting identicalgrease formulations containing, instead of the acyl p-amino phenols, twoacceptable commercially available oxidation inhibitors.

Table I.-N0rma-Hoflman bomb tests Hours To Pfrcssure Drop 0 GreaseSample Grease (no anti-oxidant) 24 52 74 Example I (N-lauroyl'p-aminophenol) 168 336 380 408 Example II (N-myristoyl p-amino phenol) 82 146155 169 Example III (N-stearoyl p-amino phenol) 48 76 83 94 Example IV(N-n-valeryl-4-amino-3 pentadecyl phenol) 125 192 215 336 Example V(N-lauroyl p-arnino phenol in ester based grease) 744 1, 480. Example V(no anti-oxldant-control) 220 Mineral oil base 1 grease with commercialInhibitor A 3 V 96 168 264 3650 Mineral oil base 1 grease withcommercial Inhibitor B 3 112 186 262 302 1 Same type base grease asgiven in'Ex-ainple I. 2 A mine complex intermediate. 3 Phenylalpha-naphthyla-minc.

An examination of the data reported in Table I above will show that thegreases of this invention compare very favorably with the commercialpreparations with the grease of Example I showing outstanding resistanceto oxidation.

A recent U. S. Army specification,Specification 2134, requires that agrease sample containing a polished copper strip imbedded therein besubjected to pounds oxidation pressure in the Norma-Hoffman bomb for 20hours without any drop in pressure and without showing any staining ordiscoloration on the copper strip itself or in the grease surroundingthe imbedded copper strip.

The experimental greases and those containing the two Table II .-ArmySpecification 2-134, Norma-Hofiman bomb test (copper catalyzed) Hours toPressure Drop oi- Discolora- Grease Sample tion Example I (noantioxidant-control grease) 14 50 Dark. Example I (N-lauroyl p-aminophenol)--- 154 220 None. Example II (N-myristoyl p-amino pheno1) 168 240None. Example III (N-stearoyl p-amino phenol) I20 150 None. Example V(N-lauroyl p-amino phenol in ester based grease) 210 310 None. Esterbasegrease (no antioxidant-control grease) .4 85 170 Dark. Mineral oilbase grease with commercial ibitor A 110 184 Slight. Mineral oil basegrease with commercial Inhibitor B 110 152 Dark.

One of the common failings of oxidation inhibitors is their instabilityto deterioration caused by sunlight. Grease compositions containingthem, therefore, darken upon exposure and lose their desired lightcolor. The experimental greases and the two grease formulationscontaining the commercial inhibitors were subjected to 40 hours ofultra-violet light exposure and their resulting color change reported onthe following basis. Black was given a rating 'of and no colorchange'was rated 0; The results of this test are set out in Table IIIbelow:

Table m. ngm stability test Grease Sample Stability Rating 1 Example I(N-lauroyl p-amino phenol) Example II (N -myristoyl p-amino phenol)..-Example III (N-stearoyl p-amino phenol) Example IV (N-n-valeryl-4-amino-3 pentadeeyl phenol) Exampl)e V (N -lauroyl p-aminophenol in ester based grease Mineral oil base grease with commercialInhibitor A Mineral oil base grease with commercial Inhibitor B UFO cocoFifty parts of a Coastal distillate having a viscosity of 55 S. U. S. at210 F. and a viscosity indexof 50 is charged to a steam heated greasekettle and heated to about 200 to 220 F. There is then added to theheated oil about 29 parts of rapeseed oil and 4.92 parts of sodiumhydroxide. When the saponification reaction is completed, l part ofp-amino phenol is added along with about 13.08 parts of the same mineraloil as was origi-' nally charged to the grease kettle. The mixture isstirred thoroughly and the temperature raised to 400 to 420 F. At thispoint the heating is stopped and about 1 part of petroleum sulfonate isadded. The mixture is then pan cooled and a lubricating grease ofexcellent structure stability and antioxidant characteristics isobtained. (All parts are given as parts by weight.)

It may be desired to add to the grease composition of this inventionother of the well known additive materials such as tackiness agents,corrosion inhibitors, other oxidation inhibitors, detergents and thelike. This may be done with impunity in the greases of this invention 6since the acylzp-amino phenols are perfectly compatible with theseadditive materials.

To recapitulate briefly, this embodiment of the present inventionrelates to lubricating grease compositions having outstandingcharacteristics of oxidation resistances which comprise a lubricatingoil, either natural occurring or synthetic, thickened to a'greaseconsistency with the metal soap of a fatty acid and which containcombined therein in a minor proportion 21 compound having the generalformulawherein R is a non-benzoid group containing from 2 to 24 carbonatoms, preferably from 10 to 18 carbon atoms, and R and R are hydrogenatoms or alkyl groups. The oxidation inhibitor may be added to thegrease composition at any stage of its manufacture or it may bedissolved in a naphthenic oil and added to a finished grease withworking at moderate temperature.

Another embodiment of this invention relates to synthetic lubricatingcompositions. Particularly this invention relates to syntheticlubricating compositions having combined therein a minor amount of anN-acyl-p-aminophenol as an oxidation inhibitor and general stabilizingagent.

In an effort to obtain superior lubricating oils having specific andunusual characteristics, new synthetic lubricants have been developed.One class of materials which has attracted unusual interest as syntheticlubricants are the esters, both the simple and complex type. In gen-veral these lubricating oils are characterized by higher viscosityindices and lower pour points than mineral oils of correspondingviscosity. Lubricants possessing such properties are of special value inthe lubrication of engines which are subjected to high temperatures suchas combustion turbine engines, particularly those of the propjet type.Mineral oil lubricants containing added viscosity index improvers, pourpoint depressors, or other highly non-volatile additives are undesirablefor use in such engines because of their tendency to leave a residuewhich accumulates and interferes with the operation of the engine. Inaddition the high pour points and low flash points of such compositionsare undesirable. The synthetic lubricants of the ester type areespecially adaptable to use under such conditions since these lubricantscontain no additive and have a desirable combination of high flashpoints, low pour points, and high viscosities. In addition they thustend to leave no residue upon volatilization.

In the past it has been found that the synthetic lubricant of the estertype, while extremely desirable due to their low pour points, high flashpoints and high viscosities, are somewhat unstable to light and have atendency to corrode the metal of bearing surfaces. These undesirableresults flow from the formation of corrosive materials formed onoxidation of the lubricant occurring under the conditions of high shearand high temperature to which they are subjected during normaloperation.

It has now been found that these undesirable qualities may be removed bythe addition to the synthetic oil as oxidation inhibiting-stabilizingagents, certain members of the family of the N-acyl-p-amino phenols.

' The lubricating compositions of this invention consist essentially ofa synthetic lubricating oil of the ester type, either complex esters orsimple esters, and a minor amount, sufficient to improve the oxidationresisting characterisiic thereof, of an N-acyl-p-amino phenol.

THE SYNTHETIC LUBRICATING on.

The lubricant used as a base for the improved compositions of' thisinvention may be any of the synthetic lubricating oils known to the art.IThese known, types include long chain esters of monobasic acids,polybasic acids, mono! and polyhydroxy alcohols, polymerized esters,ethers, ether esters, ester ethers, alkylated aromatics, polymerizedcracked wax, and the like. Of these various types of syntheticlubricants, the synthetic esters, either simple or complex, arepreferred, and are used in the formation of the preferred embodiment ofthis invention.

The synthetic esters operablein the preferred embodiment of thisinvention are those esters, distillable or not distillable, which areformed by the interaction of two or more of the following compounds:

( 1) Monohydric alcohols (2) Monobasic acids (3) Dibasic acids (4)Glycols (5) Polyhydric alcohols (6) Polybasic acids When at least onepolyfunctional alcohol and at least one polyfunctional acid areemployed, the resulting ester is known to the art as a complex ester.Diesters of dibasic acids, or single esters of monobasic acids arereferred to as simple esters.

Especially preferred among the simple esters are those esters having theformula where R and R are alkyl groups, alike or different and containfrom 1 to 20 carbon atoms, in a straight or branched chain, and where xis an integer from 2 to 10, preferably 4 to 8. These esters includethose prepared from the following acids:

Succinic acid Glutaric acid Adipic acid Pimelic acid Suberic acidAzelaic acid Sebacic acid Brassylic acid Pentaldecanedicarboxylic acidTetracosanedicarboxylic acid The C -C alkenylsuccinic acids listed aboveare prepared by condensing olefins' or mixtures of olefins with maleicanhydride.

The complex esters contemplated by this invention are grouped under thefollowing types:

Type I.-Mnobasic acid-glycol-dibasic acid-glycolmonobasic acid.-Thiscomplex ester may be considered to have the following structuralformula:

wherein R and R are the alkyl radicals of the monobasic acids; R and Rare the alkyl radicals from the glycols; and R is the alkyl radical fromthe dibasic acid.

The esters of this type are prepared by admixing the calculated amountsof the various compounds and carrying out a straightforwardesterification of the reaction. The reaction conditions are continuedwith an occasional sample of the product being tested for acidity untilthe minimum acidity is attained.

Type II.-Alcohol-dibasic acid-glycol-dibasic acid-alcohol.-This materialmay be represented by the following formula:

R OO-C+-R -C-OO- R -O--OC-R -CO--O--R wherein R and R are the combiningradicals of the alcohol; R and R are the alkyl radicals of the diabasicacids; and R is the alkyl radical of the glycol.

"8 These esters are prepared in the manner'similar to those of Type I.

Type III. Alcohol dibasic acid glycol monobasic acidr- -These esters areprepared by reacting a dibasic acid and a glycol under such conditionsthat one hydroxyl group of the glycol combines with one carboxyl groupof the dibasic acid, in other words, so that a half ester is formed.This half ester is then reacted with a molar proportion each of analiphatic alcohol and a monobasic acid. These materials may be said tohave the general formula:

wherein R and R are the combining alkyl radicals of the alcohol; R and Rthe alkyl radicals of the dibasic acid; and R is the alkyl radical ofthe glycol.

It will be noted that the esters of Type IV have the same structuralformula as Type II. However, these complex esters are prepared byreacting an alcohol with a dibasic acid under such conditions that ahalf ester is formed and reacting two moles of such an ester with onemole of a glycol.

Type V.M0n0basic acid-glycol-dibasic acid-glycolmonobasic acid-Thesesynthetic esters may be said to have the general formula:

wherein R and R are the alkyl radicals of the monobasic acid; R and Rare the alkyl radicals of the glycol; and R is the alkyl radical of thedibasic acid.

It will be noted that these synthetic esters are the same as thoseappearing above under Type I except that this type is prepared byreacting a monobasic acid with a glycol under such conditions that ahalf ester is formed and reacting two moles of such ester with one moleof a dibasic acid.

The alcohols used in forming the esters set out above, either the simpleor the complex type, include the follow ing:

Methyl alcohol Ethyl alcohol n-Butyl alcohol n-Hexyl alcohol n-Octylalcohol 2-ethylhexyl alcohol Cetyl alcohol Oleyl alcohol Ethylene glycolmono-n-butyl ether Ethylene glycol mono-Z-ethylbutyl ether Ethyleneglycol mono-Z-ethylhexyl ether Ethylene glycol mono-tert.-octyl ether,B-n-Butylmercaptoethanol S-terL-octylmercaptoethanolB-n-dodecylmercaptoethanol Diethylene glycol mono-n-butyl etherDiethylene glycol mono-2-ethylbutyl ether Diethylene glycolmono-Z-ethylhexyl ether Propylene glycol mono-butylthioether Propyleneglycol mono-tert.-octyl thioether Propylene glycol mono-n-dodecylthioether n-Butylmercaptoethoxyethanol Tert.-octylmercaptoethoxyethanoln-Dodecylmercaptoethoxyethanol 7 '9 n-ButylrnercaptopropoxypropanolTert.-octylmercaptopropoxypropanol n-DodecylmercaptopropoxypropanolPropylene glycol mono-n-butyl ether Dipropylene glycol monomethyl etherDipropylene glycol monoethyl ether Dipropylene glycol mono-n-butyl etherTripropylene glycol monomethyl ether Tripropylene glycol monoethyl etherTripropylene glycol mono-n-butyl ether Propylene glycol'monoisopropylether Dipropylene glycol monoisopropyl ether Tripropyleneglycol monoisopropyl ether Many of the above listed ether alcohols,formed by the reaction of ethylene oxide or propylene oxide withaliphatic alcohols, are known in the industry as Dowanols, Carbitols, orCellosolves.

A group of alcohols especially adapted for use in connection with thepresent invention are the so-called x0 alcohols, prepared by thereaction of carbon monoxide and hydrogen upon the olefins obtainablefrom petroleum products. Materials such as diisobutylene and C olefinsare suitable for this purpose; also higher and lower molecular weightolefinic materials are sometimes employed. The alcohols obtained in thismanner normally have a branched chain structure.

Among the monobasic acids which may be employed in the preparation ofthe esters of the present invention, the following may be listed asillustrative:

Acetic acid Propionic acid Butyric acid Valerie acid Caproic acidCaprylic acid Laurie acid Palmitic acid Stearic acid Oleic acidfl-Methoxypropionic acid fi-Ethoxypropionic acid fi-TerL-octoxypropionicacid fi-Ethylmercaptopropionic acid fi-TerL-octylmercaptopropionic acidB-TerL-dodecylmercaptopropionic acid Any of the various 0x0 acids Theglycols employed in preparing the esters of the present inventioninclude ethylene glycol and any of the parafiinic homologues of the samecontaining up to 18' carbon atoms. These may include, for example,ethylene glycol, propylene glycol, butylene glycols, pinacone,trimethylene glycol, tetramethylene glycol, pentamethylene glycol, andthe like. Since the glycols may also contain oxygen or-sulfur atoms,compounds such as diethylene glycol, triethylene glycol, thepolyethylene glycols of the formula:

wherein nvis 1 to 2 6, and .the polypropylene glycols of the generalformula: V I

where either R, or R is a methyl group and the other is hydrogen, andwhere n is 1 to 20, may likewise be employed. Glycols containing sulfuratoms in thioether linkages may also be employed, and these include sucheompounds as thiodiglycol and 1,2-bis (2-hydroxyethylmercapto) ethane.There a150 may be used glycols con- 7 taining both oxygen and sulfur insimilar linkages; such a compound is bis-2-(2-hydroxyethoxy) ethylsulfide.

OXIDATION INHIBITOR-.STABTLIZING AGENT I -In order to prepare thelubricating oil compositions of thisinve ntion the synthetic oils asdescribed above are 16 blended with a minor amount, suficieiit toimprove the stabilityand oxidation resistance characteristics thereof,of an N-acyl p-aminophenol. These phenols have the following generalformula:

wherein R represents an alkyl group having from 1 to 8 carbon atoms;wherein R and R alike or different, are hydrogen atoms or alkyl groupscontaining from 4 to 15 carbon atoms per molecule.

The general formula above is subject to the following limitations 1) Ifthe aromatic ring is substituted; that is, if R; or R are alkyl groups,R may have from 1 to 8 carbon atoms, but the sum of R+R +R must be atleast 9 and not more than 17.

(2) If the aromatic ring is unsubstituted; that is, R; and R arehydrogen atoms then R may be an alkylgroup of from 3 to 8 carbon atomsper molecule.

Of the various N-acyl p-aminophenols operable in this invention, it ispreferred to use those materials wherein R and R are hydrogen and R isan alkyl group having from 3 to 8 carbon atoms. Those compositionswherein R is an alkyl group having more than 10 carbon atoms tend tothicken the synthetic oil and if R is 1 or 2, the phenol is insoluble inmineral oils or soluble in water.

Exemplary of the preferred compounds may be mentioned the following:

N-acetyl-p-amino phenol N-butyryl p-arninophenolN-caprylyl-p-aminophenol N-propionyl-p-aminophenolN-n-acetyl-4-amino-3-pentadecyl phenol N-n-valeryl-4-amino-3-pentadecylphenol N-n-propionyl-4-amino-3-pentadecyl phenolN-n-valeryl-4-amino-2,6,ditertiary butyl phenolN-n-caproyl-4-amino-2-hexyl phenol The preparation of three of the aminophenols are set out in detail below:

Preparation of N-acetyl-p-amin0phen0l.-One mole of p-aminophenol isdissolved in 1 liter of water containing 70 g. glacial acetic acid andthe mixture heated with 120 g. of acetic anhydride on a steam bath forone hour. After cooling to room temperature the crystals which separateare recrystallized from hot water and melt at 167 -168 C.

Preparation of N-batyryl-p-aminophenol.One mole of p-aminophenol wasmixed with 1.5 moles of n-butyric acid and cc. xylene. This mixture wasrefluxed for 5 hours in a 1 liter round bottom flask equipped with acondenser and watertrap using a hemispherical mantle. A water layer of29.4 cc. was obtained in the water take-- off trap. The yield was 168.7g. of product distilling in a short path still at 218-231 C. at -1 mm.The product melted, after three crystallizations from a mixture ofacetic acid and water, at 131 C. Analysis for nitrogen gave 7.69%compared to a calculated 7.81%.

Preparation of N caprylyl-p-aminophenol.One-half mole of caprylic acidwas mixed with 0.5 mole of paminophenol and 100 cc. xylene in a 1 literflask equipped with'a water takeofi and reflux condenser. Afterrefluxing for 6 hours 7.4 cc. of water was removed or 82% of the maybeleft in solution by dissolving all but a minor:

amount of the product. V V The compounds may also be prepared in suchmanner that the desired N-acyl p-a'minophenols' may be formed in situ.Thisprepamfionmay be accomplished in the following manner; To a heatedoil solution there is added the calculated amount of a p-aminophenol.The desired acid or acid chloride is then added, the formation of theN-acyl-p-aminophenols taking place upon the addition of the acidicconstituent. After the reaction is completed the mixture is strippedwith heating and water is removed.

The amounts of the N-acyl-p-aminophenols combined with the syntheticlubricating oil to form the compositions of this invention will varybetween about 0.1% to about Table I V.-Oxidatin inhibitors indi-Z-ethylhexyl sebacate [0.5 wt. percent concentration] N-butyrylN-acetyll- Corrosion/Oxidation Stability (250 F.) None p-amiuo amino-.8-Phenothlazme phenol pentadecyl phenol Weight change, MgJcmfi:

Copper 0 +0.06 Steel 0. Aluminum Alloy" 0. Magnesium Alloy 0. CadmiumPlated SteeL +0.00. Visible Gorrosion' opper Purple. Steel Do. AluminumAlloy. Do. Magnesium Alloy Do. Cadmium Plated Steel. Do. Oil Loss,percent 6 0.88. Viscosity Change at 100 F., percent +0.16.Neutralization Number Increase 0.02. I Separation and Guinminc Sl.Separation. Oxidation Rate: ml. 02 absorbed in 4 su cessive minuteperiods of 392 F 0-0-0-0.

5.0% by weight based on the weight of the total composition. It ispreferred to use from about 0.02% to 2.0% by weight.

The preparation of the synthetic lubricating oils used in formulatingthe compositions of this invention is accomplished by known procedureswith which the artis familiar and does not constitute a part of thisinvention.

Oil blends containing the amino phenols are prepared by simply admixingthe phenoiic material in the desired amount with the base oil andheating the' mixture to a temperature slightly above the melting pointof the phenol.

Various blends according to the concept of this invention were preparedand tested as follows:

(A) Blends using as a base oil di-2-ethylhexyl sebacate:

(a) A blend of di-Z-ethylhexyl sebacate containing combined therein 0.5by weight of N-butyryl-p-aminophenol was prepared by admixing the phenolwith the oil, heating to about 135 C. and cooling. A brilliant solutionwas obtained.

(1)) A blend of di-Z-ethylhexyl sebacate containing 0.5% by weight ofN-n-acetyl-4-amino-3-pentadecy1 pheml was prepared by heating a mixtureof the two com-. ponents to about 135 C. and cooling. A clear solutionresulted.

The two compositions preparedas indicated above were submitted to thefollowing determinations:

(l) Corrosion oxidation stability test:

This test, described in detail in Military Specification MIL-O-608'l,consists briefly in submerging five metal plates of known area andweight in a bath cc. of the. sample being tested. The sample is thenraised to a temperature of 250 F., and oxygen is bubbled through thebath. At the end of 168 hours test time the metal plates are removed,the color change is observed, and the weight change per squarecentimeter calculated. The percentage of oil sample loss is determined,the percent change in viscosity at 100 F. noted, the neutralizationnumber tested and, the. change calculated. The oil sample isalsoobserved for separationland guniming.

(2) Oxidation adsorption test:

a This test was carried; outaccording to a method simia cant:

An examination of the data in Table IV above clearly points out theexcellent oxidation stabilityi characteristics of the compositions ofthis invention. The butyryl derivative of the p-aminophenol of blendA(a) gives almost perfect results in the very stringent tests describedin detail above. Only 0.01 mg./cm. of weight change was detected in thecase of magnesium alloy and all of the visible corrosion results weresatisfactory. The N- acetyl-4-amino-3 pentadecyl phenol of blend A(b)showed a loss of 0.07 mg./cm. in the case of the copper plate, theothers being satisfactory; All of the visible corrosion tests werepassing. The phenothiazine compound, the best available inhibitorheretofore known, showed weight changes of +0.06 in the case of bothcopper and the cadmium plated steel samples. These results are stillwithin the satis factory range but are not as satisfactory as either ofthe two experimental inhibitors. This compound failed all of the visiblecorrosion tests.

In the determination of the percent of oil lost during thetest, none wasshown by either A(a) or A(b), the compositions ofinvention, whereas thephenothiazine solution showed a loss of 0.88%. In the other tests thethree compositions showed outstanding results, only the phenothiazineslightly separating after the test period. No oxygen was absorbed byeither of the compositions in the stringent oxygen adsorption test.

The data of Table IV above, particularly the low amount of test plateweight loss and the lack of visible corrosion points out that thecompositions of this invention are very useful as metal deactivators andare particularly desirable in compositions that come in contact withmetals, such as insulation materials and transformer oils and the like.There may also be added to the compositions materials such as 2-aminobenzenethiol, amine type antioxidants containing metal deactivators, andthe like to enhance the metal deactivation effect of the N a-am n Phn 1(B) Blends using as a base oil a complex ester lubri- Acomplex'estenlubricating oil.prepared from 8.8 mols of rspoctylalcohol,4.4 mols of triethylene glycol and 8.0 12. 9. 1.95 ad i cid nd ha ng aor u a e sn ise Table V.Oxidatin inhibition in complex ester lubricants[0.5 wt. percent concentration] No Inhibi- N -butyryl Corrosion]Oxidation Stability (250F.) tor p-aminophenol Wt. change mgJcm z Copper-.11 None N n 0. Aluminum Alloy .05..- Do. Magnesium Alloy 4.11-- 0.06.Cadmium Plated Steel 20.90. 0.02.

Visible Corrosion te Aluminum Alloy. Magnesium Alloy Cadmium PlatedSteel-..

Separation and Cumming An inspection of the data of Table V aboveclearly points out the inhibiting effect of the N-butyryl-p-aminophenolin the complex ester type synthetic lubricant.

It is also within the concept of this invention to add other additivematerials to the improved lubricating compositions of this invention.Other oxidation inhibitors, or additive agents such as detergents, pourpoint depressants, thickeners, sludge dispersants, extreme pressureagents, corrosion inhibitors and the like are compatible with theadditive materials of invention and blends of these may be made to fitthe requirements of the lubricating job for which the oil is desired.

To recapitulate briefly, this embodiment of the invention relates to newand improved lubricating oil compositions having outstanding oxidationresistance and having exceptional high and low temperaturecharacteristics. The novel compositions comprise synthetic lubricatingoils containing combined therein minor but oxidation resistanceimproving amounts of an N-acyl p-aminophenol. The phenolic material ofthese new compositions have the following general formula:

where R is an alkyl group having 1-8 carbon atoms, R, and R alike ordifferent, are hydrogen atoms or alkyl groups containing from 4 to 15carbon atoms, and where R and R are not both hydrogen atoms, then R+R +Rmust be not less than 9 nor more than 17. The preferred phenolicmaterials are defined by the formula above when R and R are hydrogen'andR is an alkyl group of from 3 to 8 carbon atoms.

The synthetic oil base for the compositions of the invention is of theester type, either the simple esters or the complex esters. From 0.001%to 5.0% by weight of the phenolic material may be incorporated into thebase oil, preferably from 0.01% to 2.0%.

In still another embodiment of the present invention, p-acylaminophenols, particularly those wherein the hydrocarbon residue of theacyl group has at least two carbon atoms, are added to vegetable andanimal fats, oils and their derivatives such as soaps. Butter, lard,hardened fats, coconut oil and other animal and vegetable fats, fattyacids and soaps, such as the potassium and sodium salts of the fattyacids contained in these fats and fatty oils, tend to develop anobjectionable rancid odor and "14 tasteon exposure to air and, inaccordance with this embodiment of the present invention, thesematerials are stabilized against oxidation and deterioration for longperiods by addition of this class of antioxidant.

In general, the amount of anti-oxidant to be added is in the range ofabout 0.001 to 5.0 /b, preferably 0.01 to 0.5%. The concentration of theanti-oxidant may vary to secure protection against deterioration to aless or greater degree depending upon the nature of the fat, fatty oil,or soap in question, the nature of the acyl group. Preferred are theacyl aminophenols wherein the acyl group has from 9-19 carbon atoms.

The following examples further illustrate this embodiment of the presentinvention: 1

EXAMPLE VII The stabilizing effect of the inhibitor of the presentinvention upon animal fats was determined. The proteinaceous residuefrom rendering generally has been considered free from rancidityproblems although almost all who store these products are aware ofrancidity. The rapidly developing practice of adding animal fats toanimal and poultry feeds has imposed an additional requirement forstability in animal fats. This requirement stems from the vitamin andnutrient destroying capabilities of rancid fats.

In this example, all renderings were performed in a standard designAlbright-Nell dry melter. The data in the tables below were obtainedfromrendering hog meat in the melter. The materials were well washed. Inorder to evaluate the effect of adding the anti-oxidant of theinvention, the stability values reported were obtained by theaccelerated method based on formation of volatile carbonyl compounds asreported by J. F; Neurner and L. R. Dugan, Jr. in Food'Technology, vol.7, No. 5, 191-194 (1953).

In the table below there is shown a comparison of the stabilizingeffects of several anti-oxidants upon lard; In each case, 0.01% of thestabilizer was employed.

These data clearly show the considerably greater stability of the lardstabilized with the anti-oxidant of the invention.

EXAMPLE VIII In this example there is illustrated the stabilizing etfectof the p-acyl amino-phenol upon a vegetable oil. Olive oil was held at50% humidity and at F. and the odor determined at the end of 100 hours.Again, 0.01% of various anti-oxidants were employed to stabilize the oilbeing tested.

Antioxidant Odor after 100 hours 0 ontrnl 4 Butylated hydroxyanisole 12, 6 di-tertiary butyl p-cresol 1 p-lauroyl aminophenol 0 Citric aeid 44= Bad odor. 1 Very faint rancid odor. 0=San1e odor as original oil.

EXAMPLE IX Lauroyl p-aminophenol has also been found to stabilize lightcolored soap chips made with soy bean fatty acids. In this test, 10grams of soap chips at 100% humidity are held in a 200 cc. sealed glassjar at 100 F. The soap -15 containing 0.02% of the stabilizer was rancid'in 24 hours by this test, while that containing 0.05% was rancid in 7days. The un'stabilized soap was rancid in 8-12 hours.

EXAMPLE X In this example, samples of hydrogenated cotton seed oil werestabilized with p-acyl aminophenols and the resistance to oxidationmeasured by the Norma-Hoffman oxidation bomb test described previously.

Hours of Pif'essuro Drop Sample lbs. 10 lbs. lbs.

Unstabillzed +0.05% lauroyl p-amluophenol 120 240 +0.51% stearoylp-amlnophenol 100 176 212 These data show that hydrogenated vegetableoils are rendered stable to oxidation even under the relatively severeconditions of this test.

What is claimed is:

1. A lubricating grease composition consisting essentially of alubricating oil thickened to a grease consistency with a grease makingmetal soap of a fatty acid having combined therein a minor, butoxidation resistance improving amount, of a compound having theformula-- wherein R is an alkyl group having from 10 to 18 carbon 16atoms and R and R" are alkyl groups containing from 4'to '15 .carbonatoms. 4

3. A lubricatinggrease composition consisting essentially of a minerallubricating oil thickened to a grease consistency'with the sodium soapof rapeseed oil having combined therein from 0.25% to 2% by weight of N-lauroyl p-amino phenol. 1

4. A lubricating grease composition consisting essentially of a minerallubricating oil thickened to a grease consistency with the sodium soapofrapeseed oil having combined therein from 0.25% to 2% by weight of N-myristoyl p-amino phenol. V p

5. A lubricating grease composition consisting essentially of a minerallubricating oil thickened to a grease consistency with the sodium soapof rapeseed oil having combined therein from 0.25 to 2% by Weight of N-stearoyl p-ainino phenol.

6. Alubricating grease composition consisting essentially of di-2-ethylhexyl sebacate thickened to a grease consistency with the lithiurn'soapof stearic acid and having combined therein from 0.25 to 2% by weight ofN- lauroyl p-amino phenol.

7. A process for the preparation of a lubricating grease compositionhaving outstanding oxidation resistance properties which comprisesadding to a heated lubricating oil a saturated fatty acid, adding to themixture a quantity of a metallic hydroxide sufficient to form thedesired amount of a grease making metal soap of the said fatty acid andto leave a portion of the said acid unreacted, adding to the mixture aquantity of an amino phenol suificient to react With said unreacted acidand form the desired amount of acyl p-amino phenol, and stripping theresulting mixture of water to form a stabilized grease composition.

References Cited in the file of this patent UNITED STATES PATENTS1,938,456 Lan Kelma Dec. 5, 1933 2,360,631 Zimm er et a1 Oct. 17, 19442,604,450 Morway et al July 22, 1952 2,604,452 Morway et al. July 22,1952 2,625,557 Cottle et al. July 22, 1952 2,629,666 Morway et al. Feb.24, 1953 2,642,397 Morway et a1. June 16, 1953 2,654,722 Young et alOct. 6, 1953

1. A LUBRICATING GREASE COMPOSITION CONSISTING ESSENTIALLY OF ALUBRICATING OIL THICKENED TO A GREASE CONSISTENCY WITH A GREASE MAKINGMETAL SOAP OF A FATTY ACID HAVING COMBINED THEREIN A MINOR, BUTOXIDATION RESISTANCE IMPROVING AMOUNT, OF A COMPOUND HAVING THE DORMULA